[18.19] Simulations of the Cassini Radio Occultation Experiments for the Atmosphere of Saturn Based on Recent Laboratory Measurements

P. N. Mohammed, P. G. Steffes (Georgia Institute of Technology)

Studies of the sensitivity of the Cassini three frequency
radio link to the atmospheric constituents encountered
during radio occultation are being conducted using
laboratory measurements of the 9 mm opacity of phosphine and
ammonia (Mohammed and Steffes, ICARUS 166, 425-435, 2003)
and the centimeter wavelength opacity of these constituents
measured under simulated conditions for Saturn (see, e.g.,
Hoffman et. al. ICARUS 152, 172-184, 2001). A computer model
has been developed to simulate ray paths and the ray path
parameters in the atmosphere of Saturn encountered during
occultation. In conjunction with the results of the
laboratory measurements this model is used to calculate
attenuation profiles from phosphine and ammonia and excess
Doppler shift and refractive defocusing at Ka-band (32 GHz
or 9.3 mm), X-band (8.4 GHz or 3.6 cm) and S-band (2.3 GHz
or 13 cm). These parameters are being determined for ingress
and egress occultations on revolutions 7, 51, 54 and 70, the
first of which will begin May 3, 2005. The radio occultation
simulator also predicts the pressure to which each of the
three frequencies can penetrate before loss of signal.

This work is supported by the NASA Planetary Atmospheres
Program under grant NAG5-12122.